DNA sequencing of 15,843,270 of immunoglobulin heavy gene rearrangements of B cells from allergic and normal children expressing IgE gave results consistent with indirect switching to IgE from IgG or IgA expressing B cells 33, suggesting that allergen specificity and affinity of IgE in allergy is generated by somatic mutation of preformed immunoglobulin products. This evidence concerns the gene IGHE and allergic disease.